The invention relates to an apparatus for controlling attitude of an electrically driven and positioned, vehicle mounte device or devices such as a seat mechanism, a tilting or telescoping mechanism for a steering assembly, and in particular, to the protection of such an apparatus which is not provided with a detector for detecting a limit position which determines the extent of movement of a movable part.
A road vehicle is generally provided with an arrangement which facilitates every driving operation by a driver, by enabling a free adjustment of the position of a driver's seat, a steering wheel or the like. These elements are normally adjusted to assume positions used when driving the vehicle. It will be appreciated that the seat or the like is positioned to leave only only the space required for the driver to move his hand or foot, so that if the seat or the like is left in such positions, the driver cannot get on or off the vehicle without assuming a stressed attitude because of the steering wheel or seat back which stands in the way for the driver. Accordingly, there is provided an onboard attitude controlling apparatus which brings a steering assembly, including a tilting mechanism and a telescoping mechanism, both of which are electrically driven, to a retracted position when a driver gets on or off the vehicle and which brings the assembly back to its operating position during the time the vehicle is being driven, or an onboard seat rotation controlling apparatus which directs a seat toward a boarding opening by providing an electric drive which rotates the seat.
In an electric drive mechanism, in particular, one in which an on/off drive is automatically performed, it is necessary that an extent of movement for a mechanism be determined previously so that when the mechanism reaches a limit position, the drive can be stopped at such position. Otherwise, an overload will result when the mechanism reaches the limit position, causing a damage to an electric motor, a wasteful power dissipation, a destruction of the mechanism or the like. Accordingly, it is a usual practice to provide a sensor which detects an imaginary limit position which is located short of a point of abutment by the mechanism, so that the electric motor can be automatically stopped in response to the detection of the limit position. However, when electrically driven devices increase in number, a plurality of expensive sensors must be provided. In addition, locating such sensor represents a time and labor consuming operation. It is understood that a determination as to whether the mechanism has substantially reached its limit position can be made by monitoring a motor current to see if the motor is overloaded, and interrupting the energization of the motor in response to the detection of an overload, thus dispensing with a sensor. However, in this instance, the mechanism will be subject to an increased stress and the motor will experience an excessive current flow each time the mechanism reaches its limit position, thus causing adverse influence upon the mechanism as well as on onboard battery.
Therefore, it is a first object of the invention to provide an apparatus for controlling the attitude of vehicle mounted device which prevents a mechanism from being overloaded upon reaching its limit position while dispensing with a sensor or the like which is normally used to detect the limit position and also dispensing with an adjustment to establish the limit position.
In apparatus for controlling the attitude of an electrically driven device of the kind described, it is a common practice that during a manual mode, the motor is driven as long as a manual switch is turned on, and is stopped in response to the turnoff of the switch. In this manner, the on/off condition of the switch has a one-two-one correspondence to the on/off condition of the motor. With an apparatus of this kind, a fine adjustment to establish a desired attitude can be simply made when the motor is driven at a slow rate, but it takes an increased length of time when the attitude must be changed through an increased stroke. Conversely, if the motor speed is high, the attitude can be brought to a target position rapidly if it has to be changed through an increased stroke, but a quick switch operation is required, presenting a difficulty in achieving an accurate positioning of fine adjustment. In other words, inconveniences are caused if the motor speed is either high or low. When an accurate positioning is required, it is usually the practice to provide a variable speed for the motor. However, this may require an expensive motor or a complex and expensive electronic circuit. In addition, a plurality of command switches must be provided to indicate the drive at one of different speeds.
Accordingly, it is a second object of the invention to provide an apparatus for controlling the attitude of a vehicle mounted device which enables the attitude to be changed through an increased stroke and within a reduced length of time, which facilitates a fine adjustment of the attitude and which can be provided inexpensively without requiring special switches.
It will be seen that a road vehicle includes a plurality of electrically driven apparatus for controlling the attitude, which are associated with a steering assembly, a seat, mirrors or the like. Accordingly, when changing the attitude to a retracted position or returning the attitude to its normal position as the driver gets on or off the vehicle or when adjusting the attitude in accordance with the physical feature of a driver, it is preferred that the attitude of a plurality of the vehicle mounted devices be controlled. Since a drive source or electric motor has a low speed, the control of the attitude requires a relatively long time in apparatus of this kind. Accordingly, when controlling the attitude of a plurality of vehicle mounted devices, the attitude control can be completed within a reduced length of time if the plurality of vehicle mounted devices are driven simultaneously. However, when the plurality of motors are energized simultaneously, there results a current flow of an increased magnitude, which may cause a voltage drop through the wiring, causing the likelihood that the drive of the attitude controlling apparatus itself may cease or a malfunctioning may be caused in other equipment. For this reason, it has been the practice in the prior art that where the attitude of a plurality of vehicle mounted devices must be controlled, the attitude of one device is completed to stop its associated motor before the drive for another device be initiated, resulting in a considerable length of time required in establishing the desired attitude.
Accordingly, it is a third object of the invention to reduce the length of time which is required when establishing the attitude of a plurality of vehicle mounted devices while preventing the occurrence of a malfunctioning of any one of devices being controlled.